Multicolor, multilayer photographic elements are well known in the art of color photography. Usually, these photographic elements have three different selectively sensitized silver halide emulsion layers coated on one side of a single support. The vehicle used for these emulsion layers is normally a hydrophilic colloid, such as gelatin. One emulsion layer is blue-sensitive, another green-sensitive and another red-sensitive. Although these layers can be arranged on a support in any order, they are most commonly arranged with the support coated in succession with the red-sensitive layer, the green-sensitive layer and the blue-sensitive layer (advantageously with a bleachable blue-light-absorbing filter layer between the blue-sensitive layer and the green-sensitive layer) or with the opposite arrangement and no filter layer. Colored photographic images are formed from latent images in the silver halide emulsion layers during color development by the coupling of oxidized aromatic primary amine color developing agent with couplers present either in the color developer solution or incorporated in the appropriate light-sensitive layers. Color photographic elements containing dye images usually utilize a phenolic or naphtholic coupler that forms a cyan dye in the red-sensitive emulsion layer, a pyrazolone or cyanoacetyl derivative coupler that forms a magenta dye in the green-sensitive emulsion layer and an acetylamide coupler that forms a yellow dye in the blue-sensitive emulsion layer. Diffusible couplers are used in color developer solutions. Non-diffusing couplers are incorporated in photographic emulsion layers. When the dye image formed is to be used in situ, couplers are seleced which form non-diffusing dyes. For image transfer color processes, couplers are used which will produce diffusible dyes capable of being mordanted or fixed in the receiving sheet.
It is well known in the photographic art to utilize a stabilizing bath as the final step in the processing of both color films and color papers. Such baths can serve to reduce stain and/or enhance dye stability. A wide variety of different stabilizing compositions have been proposed for such use. Thus, the known stabilizing baths include those containing thiourea or a substituted thiourea as described in Kellog, U.S. Pat. No. 2,487,446 issued Nov. 8, 1949; aliphatic aldehydes as described in Harsh et al, U.S. Pat. No. 2,518,686 issued Aug. 15, 1950; addition products of formaldehyde and a urea, as described in Mackey, U.S. Pat. No. 2,579,435 issued Dec. 18, 1951; tetramethylol cyclic alcohols or ketones as described in Clarke et al, U.S. Pat. No. 2,983,607 issued May 9, 1961; glucoheptonates as described in Bard, U.S. Pat. No. 3,157,504 issued Nov. 17, 1964; carbohydrazides as described in Larson, U.S. Pat. No. 3,201,244, issued Aug. 17, 1965; amino acids as described in Jeffreys, U.S. Pat. No. 3,291,606 issued Dec. 13, 1966; mixtures of an aldehyde and an alkoxy substituted polyoxyethylene compound as described in Seemann et al, U.S. Pat. No. 3,369,896 issued Feb. 20, 1968; compounds comprising a tri(hydroxymethyl)methyl group as described in Jeffreys et al, U.S. Pat. No. 3,473,929 issued Oct. 21, 1969; and addition complexes of an alkali metal bisulfite and an aldehyde as described in Mowrey, U.S. Pat. No. 3,676,136 issued July 11, 1972. The use of more than one active agent in such stabilizing baths is also known. For example, U.S. Pat. No. 3,676,136 to Mowray describes the use of antioxidants such as glucose, galactose, sorbitol or mannitol in a stabilizing bath in addition to an aldehyde bisulfite addition complex.
Magenta dye stability is a particularly serious problem in color photography, as the magenta dye image tends to fade much more rapidly than either the cyan dye image or the yellow dye image. The darkkeeping stability of magenta image dyes derived from pyrazolone couplers is adversely affected by the presence of the coupler itself. This is particularly evident in the toe and midscale regions of the green sensitometric curve. In these areas, there is a substantial amount of the unreacted coupler. This unreacted coupler undergoes complex chemical reactions with the magenta dye.
For many years, formaldehyde has been commonly used as a stabilizing agent in photographic color processing to provide enhanced magenta dye stability. The photographic element is treated with a final bath containing formaldehyde, and the magenta-dye-forming coupler and the formaldehyde react to form a compound that does not cause dye fade. Under normal processing conditions, this reaction takes place in the drying oven. However, while formaldehyde is a very effective stabilizing agent for this purpose, its use is highly disavantageous from an ecological standpoint because of the well known ecological concerns relating to formaldehyde.
It has long been known that N-methylol compounds are effective stabilizing agents which can be employed as alternatives to formaldehyde (see, for example, U.S. Pat. No. 2,579,435). Such compounds are not subject to the same ecological concerns as formaldehyde, and therefore their use in photographic processing would be highly advantageous. However, the use of N-methylol compounds as stabilizing agents has been considered impractical heretofore, since such compounds tend to undergo polymerization during the stabilization step, with resultant build-up of a scum of polymerized material on the photographic element and on processing equipment, such as, for example, the rollers of the apparatus used in drying the element.
It is toward the objective of providing a stabilization process which renders feasible the use of N-methylol compounds on a commercial basis that the present invention is directed.